Health

Ovulation Calculator

Estimate your ovulation date and fertile window based on your last period and cycle length. For informational purposes only.

Enter the first day of your last period above

Advertisement

Ovulation Estimation Formula

Ovulation Day = LMP + (Cycle Length − 14)

Where LMP is the first day of the last menstrual period and the luteal phase is assumed to be 14 days.

Fertile Window: Ovulation day ± 5 days (the 5 days before and the day of ovulation).

Next Period: LMP + Cycle Length

How to Use This Calculator

Enter the first day of your last menstrual period and your average cycle length (typically 21–45 days). The calculator estimates your next ovulation date, fertile window, and expected next period.

This tool provides estimates based on average cycle patterns. Actual ovulation timing varies and this is not a substitute for medical advice or ovulation testing.

Frequently asked questions

When do you ovulate during your cycle?
Ovulation typically occurs about 14 days before the start of the next period. For a 28-day cycle this is day 14; for a 32-day cycle it is around day 18.
How long is the fertile window?
The fertile window is roughly 6 days: the 5 days before ovulation and the day of ovulation itself. Sperm can survive up to 5 days in the reproductive tract, and an egg is viable for 12–24 hours after release.
What are signs of ovulation?
Common signs include a slight rise in basal body temperature, changes in cervical mucus (becoming clear and stretchy), mild pelvic pain (mittelschmerz), and a positive LH surge on an ovulation predictor kit.
What is an LH surge?
The LH (luteinising hormone) surge is a rapid increase in luteinising hormone that triggers ovulation, usually 24–36 hours before the egg is released. Ovulation predictor kits detect this surge in urine.
How does cycle length affect ovulation timing?
Ovulation always occurs approximately 14 days before the next period, regardless of cycle length. A longer cycle simply means more days in the follicular phase before ovulation, not more days after.

Related calculators